Add Global and Group level labels

What does this MR do?

Add Global and Group level labels.

Are there points in the code the reviewer needs to double check?

Labels related services.

Why was this MR needed?

We'll be adding more feature that allow you to do cross-project management of issues.

Screenshots (if relevant)

• Global Labels

• Group Labels

• Project Labels

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #19997 (closed)